Alloy steel having surface free from alligatoring



United States Patent ALLOY STEEL HAVING SURFACE FREE FROM ALLIGATORING Cedric G. Mickelson, Gary, Ind., and Charles D. Asherman, Chicago, lll., assignors to American Steel Foundries, Chicago, lll., a corporation of New Jersey This invention relates to alloy steel and more particularly toalloy steel castings having good wear resistance,"

high impact strength and asmooth, defect free surface. Alloy steels have been developed having high impact values, particularly at low temperatures, and also having such properties as toughness, corrosion and wear re- 2,970,903 Patented Feb. 7, 1961 must be present, as an addition to the molten metal, in the amount of at least about 0.35% by weight of the molten metal. These percentages are critical and it should be noted that all three constituents, namely, silicon, aluminum and rare earth, must be utilized in at least the percentages indicated.

The rear earth metal addition referred to herein, is intended to mean any of the rear earth. metals, but particularly combinations thereof including lanthanum, cerium, praseodymium and neodymium, though other combinations are equally eifective.

The following typical heats of tough, high impact strength, alloy steels are given by way of example to illustrate the effect of varying the percentages of silicon, aluminum and rare earth metals on the surface condition of castings poured from the heats. The percentages given for aluminum and the rare earth metals represent an add.tion for deoxidation purposes, it being understood that the steel castings resulting from the heats will contain only the deoxidation residue.

Addition HeatNo. (3 Mn s1 P 8 Cr M0 N1 B l Rare Al Earth Metals sistance, and weldability. However, satisfactory castings utilizing these alloy steels have been produced only in relatively thin sections. When castings having sections of about four inches or greater in thickness have been poured, they have been subject to surface defects commonly called and referred to hereinafter as alligatoring.

Alligatoring may be defined as a surface condition characterized by random, irregular cracks, of vary.ng

depth, and resembling to a great extent the appearance of 40 is accentuated when the rate of cooling is decreased because in this instance, there is a greater length of time for the oxidation to occur. Factors which particularly contribute to the formation of alligatoring are casting sections of approximately four inches and upward in thickness and also the pouring of the alloy steel in sand molds, both of which have the effect of greatly reducing the rate of cooling.

The steel alloys which have the best impact and toughness characteristics but which also give the most trouble With respect to alligatoring when cast with sections in the range of four inches and thicker are those containing, as alloy constituents, one or more of the group including manganese, chromium and nickel in the following proportions:

Mn, 1.50 to 2.50%; Cr, 0.75 to 3.00%; and Ni, 0.75

It has been found, according to the present invention, that the surface defect known as alligatoring can be completely eliminated from alloy steel castings of the type referred to herein even when these castings are poured in sand molds and are cooled slowly. The invention contemplates the inclusion or addition of silicon, aluminum and rare earth metals in minimal quantities. Specifically, silicon must be present in the amount of at least about 0.60%; aluminum must be present, as an addition to the molten metal, in the amount of at least about 0.10% by weight of the molten metal; rare earth The metal from these heats was poured into green sand molds using silica sand as the molding material. The test bars comprised sections varying from about four inches to about eight inches in thickness. The castings were not shaken out until the following day at which time they had almost reached room temperature. It should be noted, however, that the shake-out temperature has no great effect on the quality of the castings.

Heat No. 1 shows a silicon content and a rear earth metal addition below the minimal quantities. Heat No. 2 illustrates an attempt to compensate for a low silicon content by a high rare earth metal addition. Heat No. 3 illustrates an attempt to compensate for a low rare earth metal addition by an extremely high silicon content. The castings from heats No. l, 2, and 3 had surfaces with moderately heavy alligator skin. However, the outer surface of the castings produced from heat No. 4 was entirely free from surface defects and no evidence of alligatoring was present.

The minimal silicon content of 0.60% together with the add tion to the molten metal of at least about 0.10% aluminum and at least about 0.35% rare earth have been found to eliminate alligatoring from casting surfaces in alloys having the following components in the ranges indicated: about 0.25 to 050% carbon; nil to about 0.025% sulphur; nil to about 0.025% phosphorus; about 0.75 to about 3.00% chromium; about 0.50 to 0.65% molybdenum; and about 0.0005 to about 0.005% boron.

We claim:

1. A high impact, wear resistant low alloy steel for heavy section castings characterized by a surface free from alligatoring, said alloy comprising silicon in the amount of at least 0.60%, said alloy steel being deoxidized by the addition to the molten metal of at least about 0.10% aluminum and at least about 0.35% rare earth, based on the weight of molten metal.

2. A high impact, wear resistant low alloy steel for heavy section castings characterized by a surface free from alligatoring, said alloy comprising silicon in the amount of at least 0.60%, said alloy steel being deoxidized by the addition to the molten metal of at least about 0.10% aluminum and at least about 0.35% 'rare" earth, based on the weight of molten metal.

3. A high impact, wear resistant low alloy steel for castings having minimum section of about four inches and-characterized by a surface free from alligatoring,

- said alloy having a silicon content of at least about0.6

I said alloy being deoxidized by the addition to the molten ;me,tal of at least about 0.10% aluminum and at least -about- 0.35% rare earth, based on the weight of molten metal.

4. A high impact, Wear resistant low alloy steel for castings having sections of about four to eight inches, characterized by a surface free from alligatoring, said alloycontaining silicon in the amount of at. least 0.60%, and the residue from the treatment of the molten metal with at least 0.10% aluminum and at least 0.35% rare earth, based on the weight of molten metal.

A high impact, wear resistant alloy steel for cast- -ings having sections of about four to eight inches, and characterized by a surface free from alligatoring, said alloycontaining about 1.50 to 2.50% manganese, about 0.75 to 3.00% chromium, about 0.75 to 3.50%, nickel, at least 0.60% silicon, and the residue from the treatment of the molten metal With at least 0.10% aluminum .and at least 0.35% rare earth based on the Weight of molten metal.

.6. An alloy steel for castings having a minimum sec: tion thickness of about four inches and having a surface "substantially free from defects, said alloy including at ,7 least one element selected from the group consisting of: manganese 1.50 to 2.50%; chromium 0.75 to 3.00%,

and nickel0.75 to 3.50%, said alloy having a silicon content of at least about 0.60%., said alloy being deoxidized by the addition to the molten metal of at least 0.10% aluminum and at least about 0.35% rare earth, based on the weight of molten-metal.

7. An alloy steel for castings having a minimum section thickness of about four inches and having a surface u s an a l e it d feats, Said a lo be o posed of about 0.75 to 2.0% oi the group consisting of manganese, chromium and nickel, and at least about 0.60% silicon, said alloy being deoxidized by the "addi- 3.00% chromium, about 1.50 to 2.50% manganese, about 0.75 to 3.50% nickel, about 0.50 to 0.65% molybdenum,

about 0.0005 to 0.005% boron, at least about 0.60%

silicon and the residue from the addition in the molten state of at least 0.10% aluminum and at least about 0.35% rare earth based on the Weight of molten metal, the balance iron.

References Cited in the file of this patent UNITED STATES PATENTS Bolkcom et al Feb. 18, 1958 Mickelson et al. Nov. 25, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,970,903 I February 7, 1961 Cedric G. Mickelson et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 1, line 41, for "Thus" read This column 2 lines 7, 8, and 40, for "rear", each occurrence, read rare column 4, line 13, for "base don" read based (SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents U$COMM-DC 

1. A HIGH IMPACT, WEAR RESISTANT LOW ALLOY STEEL FOR HEAVY SECTION CASTINGS CHARACTERIZED BY A SURFACE FREE FROM ALLIGATORING, SAID ALLOY COMPRISING SILICON IN THE AMOUNT OF AT LEAST 0.60%, SAID ALLOY STEEL BEING DEOXIDIZED BY THE ADDITION TO THE MOLTEN METAL OF AT LEAST ABOUT 0.10% ALUMINUM AND AT LEAST ABOUT 0.35% RARE EARTH, BASED ON THE WEIGHT OF MOLTEN METAL. 